Apparatus for automatic initiation of data transmission

Abstract

Early initiation of transmission of data in a network interface that includes a dedicated transmit buffer is provided in a system which includes logic for transferring frames of data composed by the host computer into the transmit buffer. The amount of data of a frame which is downloaded by the host to the transmit buffer is monitored to make a threshold determination of an amount of data of the frame resident in the transmit data buffer. The network interface controller includes logic for initiating transmission of the frame when the threshold determination indicates that a sufficient portion of the frame is resident in the transmit buffer, and prior to transfer of all of the data of the frame into the transmit buffer. The monitoring logic includes a threshold store, which is programmable by the host computer for storing a threshold value. Thus, the threshold value may be set by the host system to optimize performance in a given setting.

What is claimed is: 
     
       1. For a system transmitting frames of data across a communications medium; an apparatus comprising: buffer memory for storing data of frames composed by the host computer for transmission on the communications medium;   means, having a host system interface, for transferring data of frames to the buffer memory;   means, coupled with the buffer memory, for monitoring the transferring of data of a frame to the buffer memory to make a threshold determination of an amount of data of the frame transferred to the buffer memory;   means, responsive to the threshold determination of the means for monitoring, for initiating transmission of the frame prior to transfer of all the data of the frame to the buffer memory from the host computer;   transmit logic, responsive to the means for initiating transmission, for retrieving data from the buffer memory and supplying retrieved data for transmission on the communications medium; and   underrun control logic, which detects a condition in which the means for transferring falls behind the transmit logic, and supplies a bad frame signal to the communications medium in response to the underrun condition.   
     
     
       2. The apparatus of claim 1, wherein the transmit buffer includes a transmit descriptor ring buffer and a transmit data buffer, the transmit descriptors including data identifying data to be transmitted on the communications medium and optionally immediate data, and wherein the means for monitoring includes the immediate data in the threshold determination. 
     
     
       3. The apparatus of claim 1, wherein the buffer memory comprises a buffer independent of the host address space. 
     
     
       4. The apparatus of claim 1, wherein the transmit logic includes means for appending an error detection code to transmitted frames, and the bad frame signal comprises a corrupted error detection code. 
     
     
       5. The apparatus of claim 1, wherein the means for monitoring includes a threshold store alterable by the system for storing a threshold value, and logic responsive to the threshold value for making the threshold determination. 
     
     
       6. The apparatus of claim 5, wherein the frames have an identifiable beginning and the threshold value specifies an amount of data from the beginning of the frame. 
     
     
       7. The apparatus of claim 1, wherein the buffer includes a transmit descriptor ring buffer and a transmit data buffer, and the means for transferring includes: transmit descriptor logic for mapping transmit descriptors from the system to the transmit descriptor ring buffer; and   download logic, responsive to transmit descriptors in the transmit descriptor ring buffer, for retrieving data from memory in the system and storing retrieved data in the transmit data buffer.   
     
     
       8. The apparatus of claim 7, wherein the transmit descriptors further include immediate data to be transmitted on the communications medium, and wherein the means for monitoring includes the immediate data in the threshold determination. 
     
     
       9. The apparatus of claim 8, the transmit logic further including: logic, responsive to transmit descriptors in the transmit ring buffer and the means for initiating transmission, for retrieving data from the transmit descriptor ring buffer and transmit data buffer and supplying retrieved data for transmission on the communications medium.   
     
     
       10. An apparatus for controlling communication between a host system and a network transceiver coupled with a network, comprising: a buffer memory;   host interface means, having an interface to the host system, for transferring data between the host system and the buffer memory;   means, coupled with the buffer memory and including a host system alterable threshold store for storing a threshold value, for monitoring the transferring of data of a frame to the buffer memory to make a threshold determination of an amount of data of the frame transferred to the buffer memory; and   means, responsive to the threshold determination of the means for monitoring, for initiating transmission of the frame, prior to transfer of all the data of the frame to the buffer memory from the host computer;   network interface means, having an interface to the network transceiver and responsive to the means for initiating, for transferring data between the buffer memory and the network transceiver for transmission; and   control means, coupled with the network interface means, for posting status information for use by the host system, as feedback for optimizing the threshold value.   
     
     
       11. The apparatus of claim 10, wherein the host interface means includes: transmit descriptor logic for transferring transmit descriptors identifying data to be transmitted from the host system to the buffer memory; and   download logic, responsive to transmit descriptors in the buffer memory, for retrieving data from memory in the host system and storing retrieved data in the buffer memory.   
     
     
       12. The apparatus of claim 11, wherein the transmit descriptors include immediate data. 
     
     
       13. The apparatus of claim 12, wherein the means for monitoring includes logic for determining amounts of immediate data in transmit descriptors. 
     
     
       14. The apparatus of claim 12, wherein the means for monitoring includes logic for determining an amount of immediate data in a transmit descriptor and an amount of data retrieved by the download logic in response to the transmit descriptor in making the threshold determination. 
     
     
       15. The apparatus of claim 10, wherein the control means further includes: underrun control logic, which detects an underrun condition in which the host interface means in transferring data to the buffer memory falls behind the network interface means in transferring data to the transceiver, and means for supplying a bad frame signal to the communication media in response to the underrun condition.   
     
     
       16. The apparatus of claim 15, wherein the control means includes means for appending an error detection code to transmitted frames, and the bad frame signal comprises a corrupted error detection code. 
     
     
       17. The apparatus of claim 15, wherein the status information posted by the control means includes an indication of an underrun condition. 
     
     
       18. An apparatus for controlling communication between a host system and a network transceiver coupled with a network, comprising: a buffer memory, including a transmit descriptor buffer for storing transmit descriptors identifying data in the host system to be transmitted and including immediate data, and a transmit data buffer for buffering data of frames transferred from the host system;   host interface means, having an interface to the host system, for transferring transmit descriptors and data of frames between the host system and the buffer memory and including means, responsive to transmit descriptors in the transmit descriptor buffer, for downloading data of frames from the host system to the transmit data buffer;   means, coupled with the buffer memory, for monitoring the immediate data in transmit descriptors in the transmit descriptor buffer and the downloading of data of a frame to the transmit data buffer to make a threshold determination of an amount of data of the frame transferred to the buffer memory; and   means, responsive to the threshold determination of the means for monitoring, for initiating transmission of the frame, prior to transfer of all the data of the frame to the buffer memory from the host computer;   network interface means, having an interface to the network transceiver and responsive to the means for initiating, for transferring data between the buffer memory and the network transceiver for transmission; and   underrun control means, coupled with the network interface means, for detecting an underrun condition in which the host interface means in downloading data to the transmit data buffer falls behind the network interface means in transferring data to the transceiver, and for supplying a bad frame signal to the network transceiver in response to the underrun condition.   
     
     
       19. The apparatus of claim 18, wherein the means for monitoring includes a threshold store alterable by the system for storing a threshold value, and logic responsive to the threshold value for making the threshold determination; and the underrun control means includes means for posting status information which may be used by the host system as feedback for optimizing the threshold value. 
     
     
       20. The apparatus of claim 18, wherein the network interface means includes means for appending an error detection code to transmitted frames, and the bad frame signal comprises a corrupted error detection code. 
     
     
       21. A network interface adapter for a carrier sense, multiple access network with collision detection (CSMA/CD), comprising: buffer memory which stores data of frames composed by a host computer for transmission on the network;   data transfer circuitry, having a host system interface, for transferring data of frames to the buffer memory;   logic, coupled to the buffer memory, which monitors the transferring of data of a frame to the buffer memory to make a threshold determination of an amount of data of the frame transferred to the buffer memory;   a medium access controller for the CSMA/CD network coupled to the buffer memory for managing transmission of frames of data from the buffer memory to the network; and   logic, responsive to the threshold determination of the logic which monitors the transferring of data to the buffer memory, which initiates transmission of the frame from the buffer memory to the medium access controller prior to transfer of all of the data of the frame to the buffer memory, including logic which initiates transmission of the frame when no complete frame of data is present in the buffer memory.   
     
     
       22. The adapter of claim of 21, wherein the buffer memory includes a transmit descriptor ring buffer and a transmit data buffer, the transmit descriptors including data identifying data to be transmitted on the network and optionally immediate data, and wherein the threshold logic includes the immediate data in the threshold determination. 
     
     
       23. The adapter of claim 21, wherein the threshold logic includes an alterable threshold store which stores the threshold value, and logic responsive to the threshold value for making the threshold determination. 
     
     
       24. The adapter of claim 23, wherein the frames have an identifiable beginning and the threshold value specifies an amount of data from the beginning of the frame. 
     
     
       25. The adapter of claim 21, further including: underrun control logic, which detects a condition in which the data transfer circuitry falls behind the medium access controller, and supplies a bad frame signal to the network in response to the underrun condition.   
     
     
       26. The apparatus of claim 25, wherein the medium access controller includes logic which appends an error detection code to the transmitted frames, and a bad frame signal generated by the underrun control logic comprises a corrupted error detection code.